Without getting too long winded here, bought a complete M16A4 style rifle last spring from a mfg everyone would recognize. Couldn’t get a BZO. Sent the upper back and the mfg said they adjusted the front sight which I assume was canted.
I can zero the rifle now (using a Marine style 25 yard BZ), but doing so requires me to crank the windage adjustment on the carry handle rear sight almost completely to the left (there are a couple of clicks left). The POI is on target.
Is that acceptable and in spec, in terms of quality that someone should expect for a AR-15? Am I being too picky? If it zeros, just be happy and shoot it?
Hell no. You can’t adjust the front sight. The index pin on the barrel extension and the FSB are permanently where they will always be.
There’s a spec for the military’s acceptance I read somewhere along the way. It’s like 10-12 clicks off of mechanical zero. I had a bushmaster upper receiver that was like 10 clicks off of mechanical zero, and I replaced it. I knew it was the upper because I’d had that barrel work fine on another upper. Eff that!! I trued the receiver face and it got like 1 more click worse. No way. I can’t live with that slop at all.
There are potential problems beyond the obvious eye sore of a wonky upper half. I Don’t know why the bushcrapper upper was crooked, but if the bolt isn’t locking into the barrel perpendicular, the lugs aren’t locking evenly and correctly.
OK you folks convinced me. Called, got an RMA, and put the upper in a box and dropped off at UPS to go back to the factory.
Requested a replacement but I assume I have no real say. If they claim it’s fixed and send it back to me, I can’t do much except complain and never place another order from them again.
I got a new HBAR in 90 and when I zeroed it at 100 yards I had two clicks left. I called Colt, they said to send it back and I did and they put on a new barrel. It is not uncommon to get a crooked bore internally.
If they return it and there’s no change, you could try another upper receiver. That was my issue. I just happened to know it because they barrel was in another upper without the problem.
However if the FSB is reamed out of top dead center, there’s no fix that I know of. The index pin/barrel extension is nearly permanently in place, and the FSB ream job can’t be adjusted.
No in spec gun I’ve ever worked on had any play in the index pin notch… definitely not enough to make up for a windage issue. Maybe a couple thousandths, but they generally lock up with little play at all.
And there’s zero room for taper pin adjustment that I can see. I mean… that FSB goes on ONE way, exactly where the pins and FSB were reamed. A small pin would just seat deeper, and a larger pin more shallow, but the holes line up one way.
John Thomas for one has fixed stuff like that before. Pretty sure he is not alone but he gets mentioned (and praised) a lot for that sort of work on the internet. It can be done…
Fitting / Shimming an index pin notch is something that is sometimes done as well.
This - you can open up the index pin notch on the receiver a bit so the barrel can rotate, or file one side of the barrel index pin. The gap on the other side can be filled with a thin stainless steel shim which will be captured once you install the barrel nut. But, before you do that, you can determine whether the barrel is rotated in the receiver or the front sight tower is leaning by looking at the feed ramps. If the feed ramps line up perfectly, then it’s the front sight tower that’s leaning. You usually do have a little bit of rotation to play with for feed ramp alignment if you do want to make the adjustment.
Years ago, I was told by a big manufacturer that 13 clicks from center to zero windage was acceptable for a rear sight. I’ve seen rifles and carbines made by the same company require the rear sight to be adjusted all the way to the left to zero.
I’ve reindexed a considerable number of barrels to get the rear sight to no wind zero with the rear sight centered. It shouldn’t have to be done on an expensive rifle or carbine made by a company that is popular on M4C, but it is more commonplace than I think acceptable.
Years ago, I was told by a big manufacturer that 13 clicks from center to zero windage was acceptable for a rear sight. I’ve seen rifles and carbines made by the same company require the rear sight to be adjusted all the way to the left to zero.
I’ve reindexed a considerable number of barrels to get the rear sight to no wind zero with the rear sight centered. It shouldn’t have to be done on an expensive rifle or carbine made by a company that is popular on M4C, but it is more commonplace than I think acceptable.
I absolutely DO NOT want that gun. That is an unacceptable work around to me… Especially going back to my example where it is not the FSB pinned off of TDC, but the receiver is not straight.
If someone here bought a gun, took it apart and saw that crap??? There’d be hell to pay for the manufacturer sneaking that crap into a customer’s hands.
Agreed - if the whole assembly is from one manufacturer then send it back. And, good quality components should need no such alteration. But, sometimes when piecing together a frankengun; the kitchen gunsmith methods can help.
Does the front sight base appear to be canted to the left when the rear sight is held level? If you look at the muzzle, does the bore appear to be off center?
This is hard to tell. At least for me. And FSB forging “ears” are not always symmetrical where you could put a level on top.
If you look at the muzzle, does the bore appear to be off center?
This would be a unusual since the blanks are shaped after gun drill. (unless this is a Hammer Forge barrel of course) We did have a shillen barrel on a bolt gun that supposedly had this problem though.
Could be just a bad barrel that throws bullets left/right.
I can’t imagine getting an untrue FSB ream if they used a real reaming station. And if it’s BCM or FN, they’d both surely be using this tooling.
It seems like this problem used to be more commonly reported in the past. I doubt they’ll tell him what the problem is, but now I’m curious.
You mentioned above what the military deemed as ‘acceptable’ I believe. And you also mentioned selling one that you bought that was 10 clicks off? (that still falling inside of what you said the military would accept)
Plenty of other guys around here that would be able to diagnose the problem and possibly correct it on their own without selling or returning anything…
Point being - Depending on the problem and the severity - Sometimes that stuff can be adjusted / tweaked to the point where everything is perfect.
All of the parts we are discussing have ‘tolerances’ and there is no shame in having a shim here or there to make things closer to being perfect for a customer or an owner.